In this blog post, we’ll explore whether tiny robots capable of moving through the human body for therapeutic purposes are actually feasible, focusing on how micro-robots are built, how they operate, and the physical phenomena that play a crucial role in the microscopic world.
Were robots floating inside the body just science fiction?
When we think of science fiction, many things come to mind. The field is diverse, ranging from space colonies to underwater cities and robots that converse with humans. Among these is the idea of robots floating inside the human body to provide medical treatment. The concept of such robots has been around for a long time. Films like ‘Fantastic Voyage (1966) and ‘Inner Space’ (1987) demonstrate that people have long imagined miniature devices and robots operating inside the human body.
Technologies such as robots floating inside the human body, as described above, are closely related to microsystem technologies like MEMS (Micro Electro Mechanical Systems). MEMS is a field that deals with systems in the microscopic world, including the fabrication of tiny structures and their application across various fields. The structures primarily handled in MEMS are extremely small, ranging in size from the thickness of a human hair down to even smaller scales. MEMS technology has grown alongside advancements in semiconductor manufacturing processes and is currently being actively researched in various fields such as medicine, sensors, machinery, and electronics.
Given the current pace of scientific and technological advancement, what was once considered mere science fiction is no longer just an impossible fantasy. So, is the idea of a tiny robot moving through blood vessels actually feasible? In fact, research on medical microrobots is exploring methods to control their movement using external magnetic fields and deliver drugs to specific sites. However, this technology has not yet been perfected into a versatile robot capable of moving freely inside the human body; for actual clinical application, several challenges—such as precise movement and tracking, biocompatibility, and safety—must be overcome. Therefore, before assessing this possibility, it is necessary to understand how microrobots are manufactured and how they are operated after production.
How Are Micro-Robots Made?
The process of creating small-scale robots differs significantly from that of building robots of the size we commonly see, starting with the manufacturing process itself. When building a robot as we typically imagine it, we first manufacture the entire robot in separate parts. The manufacturing method involves machining materials and then assembling the individual components. These completed parts are then assembled to form a single robot. However, it is generally difficult to use this method for microstructures because the assembly process itself is challenging. Since the parts to be assembled are extremely small, moving them after fabrication and positioning them precisely presents significant difficulties. For this reason, when building micro-robots, engineers often minimize the assembly process and instead fabricate the entire structure in one go. The fabrication of micro-robots utilizes methods such as semiconductor processes or microfabrication technologies, with various fabrication methods employed depending on the structure and materials.
When fabricating larger robots, physical machining methods such as drilling and turning are used. In contrast, it is difficult to apply these methods directly to micro-robots because it is challenging to machine specific areas with precision, and there are also issues with productivity. Therefore, microfabrication primarily relies on chemical and microfabrication processes that allow the entire structure to be processed in a single step. However, this approach—introduced to avoid the two issues mentioned earlier—gives rise to another problem. Chemical processes may involve high temperatures and sometimes require the use of strong acids or bases. There is a risk that other parts may be unintentionally damaged during these processes. Consequently, when manufacturing micro-robots, each process must be carefully considered to prevent such issues, and the manufacturing process is subject to many constraints. For this reason, manufacturing micro-robots is much more difficult than manufacturing robots of standard size.
Do the laws of physics change as size decreases?
So, are the manufacturing challenges described above the only obstacles to building micro-robots? Of course not. There is another factor that must be considered with equal importance. This involves taking into account the physical laws governing the system and the effects associated with size. This does not mean that the physical laws we are familiar with change completely in the microscopic world; rather, it means that even within the same physical laws, the relative influence of each force varies significantly depending on the size of the object. In other words, robots of the typical size we are accustomed to seeing are designed with significant consideration given to factors such as gravity and inertia. In contrast, with micro-robots, the effects of gravity become relatively minor, while the influence of forces such as surface forces and viscous forces becomes relatively greater; therefore, these factors must be given careful consideration. In fact, when studying the motion of micro-robots, the viscosity of the surrounding fluid and the forces generated at the surface are key factors.
In nature, too, we can observe interesting phenomena resulting from these size effects. Ants, for example, can carry loads several times heavier than their own body weight. On the other hand, if an ant becomes trapped on a small water droplet or the surface of a liquid, it is greatly affected by surface forces and often cannot escape easily. In contrast, while a person may find it difficult to lift a load close to their own body weight, they can easily enter and exit a bathtub filled with water. Why do ants appear to withstand the effects of gravity relatively better than humans, yet be so greatly affected by surface forces? We can understand this principle by examining how gravity and surface forces vary with size. Gravity is proportional to an object’s mass, and for objects of the same density, mass is proportional to volume. Therefore, as an object’s size decreases, the magnitude of the gravitational force decreases rapidly in proportion to its volume. On the other hand, the force acting on a surface generally has a component proportional to the surface area; thus, for objects of the same shape, it tends to be proportional to the square of the length. Consequently, as the length of an object decreases, the relative influence of surface forces increases compared to that of gravity.
Let’s consider this relationship using a cube. If we let L be the length of one edge of a cube, its volume is proportional to L³ and its surface area is proportional to L². Therefore, as the object becomes smaller, the gravitational force—which is proportional to volume—decreases more rapidly than the force related to surface area. For example, when one edge of a cube is 1 m, the volume is 1 m³ and the surface area is 6 m². If we reduce the side length to 1 cm, the volume becomes 1 cm³, or 10⁻⁶ m³, and the surface area becomes 6 cm², or 6×10⁻⁴ m². The key point here is not simply comparing the ratio of these two values, but rather that as the size decreases, the volume decreases as the cube of the length, while the surface area decreases as the square of the length. Therefore, as an object becomes smaller, the relative effect of surface forces increases compared to gravity, and consequently, the relative importance of these forces changes. This principle helps us understand why small creatures, such as ants, can lift objects that are considerably heavier relative to their own body weight. Thus, when designing micro-robots, unlike robots of typical size, it is essential to consider physical effects that become significant in microenvironments, such as forces arising from surfaces and fluid viscosity.
There are various phenomena related to surface forces. Among them, one phenomenon that is particularly significant in microenvironments is surface tension. Surface tension is a phenomenon caused by intermolecular interactions at the surface of a liquid, and the behavior of an object when it comes into contact with a liquid varies depending on how well its surface interacts with the liquid.
The phenomenon described in the previous example—where small organisms cannot easily escape from water or liquid droplets—is also related to these surface effects. One method of applying surface properties to micro-robots involves chemically or physically treating the surface to alter its interaction with water or the surrounding environment. Controlling interactions with liquids through surface treatment can help reduce the force required to operate a robot underwater or within a liquid. Furthermore, when attaching a specific structure to a target object, appropriately adjusting the properties of both surfaces—such as hydrophilicity or hydrophobicity—can alter adhesion or wettability. By effectively utilizing these properties, the movement and attachment of micro-robots can be controlled more efficiently.
Could robots inside the body become a reality?
While even the robots we commonly see in daily life are difficult to manufacture, micro-robots are far more challenging to produce and control because they are subject to physical phenomena that are rarely encountered in our everyday environment. Not only in manufacturing but also during operation, researchers must account for phenomena—such as surface forces, viscous forces, and magnetic forces—whose relative effects differ significantly from those on robots of typical size; therefore, much research is still needed. In particular, active research is currently underway on methods such as using external magnetic fields to move or rotate micro-robots, as well as using them to deliver drugs to target sites; some studies have even advanced to the stage of delivering therapeutic agents to specific locations within animals. However, challenges remain, such as safely and accurately maneuvering micro-robots to desired locations within human blood vessels or tissues, tracking their positions in real time, and safely removing or degrading the robots or their components after treatment is complete.
If we can overcome the difficulties in fabrication and propulsion, as well as the challenges of ensuring safety and precise control within the body, the idea of inserting small robots into our bodies to diagnose or treat diseases will move closer to reality rather than remaining mere science fiction. In fact, research on the targeted drug delivery and in-body movement of magnetic-driven medical micro-robots has continued to advance even after 2025, and research in this field is ongoing—as evidenced by the 2026 publication of a study on magnetically driven micro-robots for the gastrointestinal tract. Therefore, while therapeutic robots floating inside the human body are not yet a technology used as freely as in movie scenes, it is also difficult to view them as a technology confined solely to the realm of past science fiction.
